Diagnostic pathway

IBS CounSEL diagnostic pathway for IBS

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IBS is an affirmative, symptom-based diagnosis1

IBS is NOT a diagnosis of exclusion2

IBS diagnostic pathway1,2

This pathway is for guidance only and is not a validated tool for IBS diagnosis. This is not intended as a substitute for clinical judgment. Each healthcare provider is solely responsible for any decisions made or actions taken in reliance of this information

Patient assessment1-3

Patient history

The following are important to consider when taking a history from a patient with possible symptoms of IBS:

  • Predominant/most bothersome symptom
  • Dietary habits and relationship of symptoms to food or stress
  • Time course of the symptoms (chronicity)
  • Other intestinal symptoms or conditions. Common co-existing disorders include dyspepsia and GERD
  • Extra-intestinal symptoms or conditions. Common co-existing conditions include fibromyalgia, fatigue, and migraine
  • Psychiatric comorbidity (e.g. anxiety, depression)
  • Family history, including history of abuse

Physical exam

Although a physical exam is normal in the majority of patients with IBS, a rectal and pelvic exam can serve to:

  • Reassure the patient
  • Exclude alternative diagnoses
  • Identify pelvic floor dysfunction
Diagnostic evaluation and differential diagnosis

What alarm features should I look for in patients with symptoms of IBS, and what might they mean?1-4

Family history of colorectal cancer, IBD, or celiac disease
Nocturnal diarrhea that awakens the patient
Onset >50 years of age
Recent antibiotic use
Rectal bleeding
Unintentional weight loss (>10% of body weight)
Persistent frequent diarrhea without hematochezia
Persistent bloating and diarrhea unresponsive to dietary interventions
Potential differential diagnosis warranting further investigation
Celiac disease, IBD, colon cancer
Celiac disease, IBD, colon cancer
Colorectal cancer, IBD, microscopic colitis
Microscopic colitis, colon cancer
Clostridium difficile colitis
IBD, colon cancer, hemorrhoids, ischemic colitis
IBD, celiac disease, colon cancer
Bile acid malabsorption
Small intestinal bacterial overgrowth

Other possible diagnoses that may need to be considered based on a patient’s specific history and symptoms include:

  • Chronic constipation
  • Narcotic bowel syndrome
  • Abdominal wall pain
  • Defactory disorder
  • Endometriosis

Presence of abdominal pain or discomfort is a key differentiator between IBS-C and chronic constipation2

In the absence of alarm features, what diagnostic tests are available in order to diagnose IBS?

In the absence of alarm features, extensive diagnostic testing is NOT required to diagnose IBS1,2,4

Common diagnostic tests often performed in patients suspected of having IBS have a very low diagnostic yield3,4

Diagnostic testing in patients with symptoms of IBS1-8

Patient history: Including family history of inflammatory bowel disease/colon cancer, discussion of dietary habits, potential symptom triggers, impact of symptoms on quality of life, and assessment for psychiatric comorbidity

Physical examination: An abdominal and digital rectal examination should be performed to help assess for stool blocking the rectum, anal strictures, masses, or structural abnormalities

Routine laboratory blood tests: CBC and CRP should be considered. Anemia may indicate a need for additional tests or alternative diagnoses

Celiac blood screening: Should be considered in patients with diarrhea as their predominant symptom

Colonoscopy/sigmoidoscopy: Not recommended unless there are other alarm features that warrant further investigation

Additional blood tests: There is little evidence that testing for serum chemistries has any diagnostic value for IBS

Allergy testing: Immunologic evidence of a food allergy is extremely rare in IBS

Stool testing for intestinal parasites: Not recommended unless specific history suggests it is warranted

Thyroid function tests: Thyroid dysfunction is not more common in patients with IBS

Lactulose breath testing: Several studies have found the prevalence of lactose malabsorption in patients with IBS to be the same as in the normal population

Symptom-based diagnosis of IBS

The validated Rome criteria are recommended to diagnose IBS1:

If there is no definitive test, how can I be confident in my diagnosis?

  • These established symptom-based diagnostic criteria have a 98% positive predictive value for IBS5
  • This means that another condition is masquerading as IBS in only 2% of cases if the patient’s symptoms meet the Rome criteria5
  • Appropriate additional testing should be conducted in patients with alarm features or other specific features that warrant investigation1,2

My patient meets the criteria for IBS; should I conduct more extensive tests so I don’t miss something more serious?

Cancer is no more common in patients with IBS than in controls3

  • Among patients meeting symptom-based criteria for IBS, the pretest probability of IBD or colorectal cancer is <1%3

Although often conducted to reassure patients, a negative colonoscopy is not associated with reassurance or improved quality of life in patients with IBS7

Subtyping IBS

Appropriate management of IBS requires accurate diagnosis of the patient’s IBS subtype1,2

IBS subtypes are based on the predominant stool form pattern1,2

IBS subtyping should be established when the patient is not taking medications used to treat constipation or diarrhea1

The Bristol Stool Form Scale is a validated descriptor of stool form and consistency

Modified from original version, © 2006 Rome Foundation. Used with permission.

IBS-C: constipation predominant
>25% hard or lumpy (BSFS types 1 and 2)

IBS-D: diarrhea predominant
>25% loose or watery (BSFS types 6 and 7)

IBS-M: mixed stool pattern >25% hard or lumpy (BSFS types 1 and 2) and >25% loose or watery (BSFS types 6 and 7)

Download the Bristol Stool Form Scale


The information on this page is for informational purposes only and is not a substitute for clinical judgment. Each healthcare provider is solely responsible for any decisions made or actions taken in reliance of this information

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  1. Lacy BE et al. Gastroenterology 2016; 150:393-1407.
  2. Longstreth GF et al. Gastroenterology 2006; 130: 1480-1491.
  3. American College of Gastroenterology Task Force on Irritable Bowel Syndrome. Am J Gastroenterol 2009; 104: S1-S35.
  4. Lacy BE. Int J Gen Med 2016; 9: 7-17.
  5. Vanner SJ et al. Am J Gastroenterol 1999; 94: 2912-2917.
  6. Cash BD et al. Am J Gastroenterol 2002; 97: 2812-2819.
  7. Spiegel BM et al. Gastrointest Endosc 2005; 62: 892-899.
  8. Simrén M, Stotzer P-O. Gut 2006; 55: 297-303.